<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">

    <title>Title</title>
    <style>
        div{
            border: 1px solid #000;
        }
        /*#：id选择器   .：类选择器*/
        #mainDiv{
            width: 1000px;
            height: 600px;
            /*居中*/
            margin: auto;
        }
    </style>
</head>
<body>
<div id="mainDiv" >
    <div style="height: 80px">
        <h1>标题栏</h1>
    </div>
    <div style="height: 516px;display: flex">
        <div style="width: 150px;height: 515px">
            导航栏<br>
            <a href="news.html" target="contentFrame">新闻</a><br>
            <a href="sport.html" target="contentFrame">体育</a>
        </div>
        <iframe name="contentFrame" width="840" height="515" src="3.html">
        </iframe>
    </div>
</div>

</body>
</html>